import 'dart:ui' as ui;
import 'dart:typed_data';

import 'package:flutter_test/flutter_test.dart';

void main() {
  TestWidgetsFlutterBinding.ensureInitialized();
  test(
    'glass samples and bends background pixels while keeping the centre stable',
    () async {
      const width = 160, height = 100;
      final sourceRecorder = ui.PictureRecorder();
      final sourceCanvas = ui.Canvas(sourceRecorder);
      for (var x = 0; x < width; x++) {
        sourceCanvas.drawRect(
          ui.Rect.fromLTWH(x.toDouble(), 0, 1, height.toDouble()),
          ui.Paint()..color = ui.Color.fromARGB(255, 40 + x, 70, 90),
        );
      }
      final sourcePicture = sourceRecorder.endRecording();
      final source = await sourcePicture.toImage(width, height);
      final program = await ui.FragmentProgram.fromAsset(
        'shaders/liquid_glass.frag',
      );
      final shader = program.fragmentShader()
        ..setFloat(0, width.toDouble())
        ..setFloat(1, height.toDouble())
        ..setFloat(2, 0)
        ..setFloat(3, 0)
        ..setFloat(4, width.toDouble())
        ..setFloat(5, height.toDouble())
        ..setImageSampler(0, source);
      Future<ui.Image> draw(double strength) async {
        shader.setFloat(6, strength);
        final recorder = ui.PictureRecorder();
        ui.Canvas(recorder).drawRect(
          ui.Rect.fromLTWH(0, 0, width.toDouble(), height.toDouble()),
          ui.Paint()..shader = shader,
        );
        final picture = recorder.endRecording();
        final image = await picture.toImage(width, height);
        picture.dispose();
        return image;
      }

      final plain = await draw(0), refracted = await draw(1);
      final a = (await plain.toByteData())!,
          b = (await refracted.toByteData())!;
      int red(ByteData data, int x) => data.getUint8((50 * width + x) * 4);
      expect(red(a, 12), closeTo(52, 1));
      expect((red(b, 12) - red(a, 12)).abs(), greaterThan(3));
      expect(red(b, 80), closeTo(red(a, 80), 1));
      expect(b.getUint8((50 * width + 12) * 4 + 3), 255);
      shader.dispose();
      plain.dispose();
      refracted.dispose();
      source.dispose();
      sourcePicture.dispose();
    },
  );
}